Photo switching

Photo-Switching Spiropyrans and Related Compounds Jonathan Hobley, Martin J. Lear, and Hiroshi Fukumura... 

Photoswitching of ionic and mechanical processes, iono-photo and mechano-photo switching, will be considered below. 

The insertion of a photosensitive group or of a redox active unit into the push-pull system 1 yields switchable molecular wires and push-pull molecules that contain a photo-switch or a redox switch S, as represented in 4. Compounds of such type containing for instance electroactive ferrocene groups and photosensitive metal complexes, have been synthesized. Some of them are shown in series 5 (Marczinke, B. Przibilla, K.J. Lehn, J.-M., unpublished data). 

The term photochromism can be defined as a light-driven reversible transformation between two isomers possessing different absorption spectra.111,21 The two isomers differ from one another not only in their absorption spectra, but also in their geometrical structures, oxidation/reduction potentials, refractive indices, and dielectric constants. When such photochromic chromophores are incorporated into functional molecules, such as polymers, host molecules, conductive molecular wires, or liquid crystals, the functions can be switched by photoirradiation.[3 61 Photostimulated reversible changes in refractive index can also be applied to optical waveguide switching.171 This chapter reviews applications of photochromic chromophores, especially diar-ylethene derivatives, in various photo switching molecular systems. 

When such photo switching chromophores are immobilized on an electrode, vectorial electron flow from the electrode to electroactive species in solution can be controlled by photoirradiation.[37,38] Using an n-octadecanethiol-modified gold electrode incorporated with diarylethene 28a, it was possible to switch vectorial electron transport from the electrode to hexacyanoferrate(m) in solution by photoirradiation. 

Other photochromic polypeptide systems have been described, in which the ability to photocontrol the specific conformation of polypeptides is an essential feature in the design of biomaterials for devices that can be photo switched. 

In the previous photoswitches, a radical unit is placed at each side of the diarylethene photo switching unit and separated by an extended it-conjugated chain. When the jr-conjugated chain length between the radical becomes longer, both photocyclization and cycloreversion reactivities are reduced. This is attributed to the reduced excitation density at the central diarylethene unit [69]. The excitation... 

Einaga Y. Photo-switching magnetic materials. J Photochem Photobiol C Photochem Rev 2006 7 69-88. 

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